1. Field of the Invention
The present invention relates to a miniature switch device with tactile effect which can be integrated in a printed circuit, particularly for forming a keyboard with ultra flat keys.
2. Description of the Prior Art
Generally, switch devices have already been proposed, particularly by the patents U.S. Pat. Nos. 4,083,100, 4,468,542 and EP-A-0 100 875, forming electric contacts between conducting areas of the printed circuit by resilient deformation of metal caps in the form of skull caps.
Usually, each of these caps is placed on the printed circuit so as to be in electric contact by its periphery with a first conducting area and to extend above a second conducting area electrically isolated from the first one and placed substantially opposite the central zone of the cap, this second conducting area being formed conventionally of a metallized bore.
Connection of the cap to the printed circuit is then provided by three studs acting at three points on its periphery, 120.degree. apart (cf U.S. Pat. No. 4,083,100).
It is obvious that by exerting on the cap a pressure oriented towards the printed circuit, deformation of this cap is caused until its central portion abuts at the end of travel against the second conducting area and provides its electric connection with the first conducting area.
However, such devices do not produce a tactile effect of the type usually desired in switches of this kind. In fact, the resistant force which the cap opposes to operation increases continuously until it exactly counterbalances this operating force, when the central portion of the cap abuts at the end of travel against the second conducting area.
This is why such devices require the use, in the connection between the cap and the key which is usually associated therewith, of relatively complex means, difficult to form and consequently expensive which are intended to produce the desired tactile effect.
The use of such means has the further drawback of appreciably increasing the thickness of the keyboard, which is contrary to the desired result.